The present invention relates to a Group III-V compound semiconductor comprising, at least, a substrate, a buffer layer and a Group III-V compound semiconductor crystal layer of the general formula InxGayAlzN (wherein, 0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1), in this order. The invention also relates to a method of producing the semiconductor.
As materials of light-emitting devices such as light-emitting diodes of ultraviolet or blue, laser diodes of ultraviolet or blue, and the like, there are known Group III-V (of the Periodic Table) compound semiconductors having a Group III-V compound semiconductor crystal layer of the general formula InxGayAlzN (wherein, x+y+z=1, 0≦x≦1, 0≦y≦1, 0≦z≦1). Hereinafter, x, y an z in this general formula are sometimes designated as the InN crystal mixing ratio, GaN crystal mixing ratio and AlN crystal mixing ratio, respectively. The Group III-V compound semiconductors particularly containing InN in an amount of 10% or more in terms of the crystal mixing ratio can control light-emitting wavelengths in the visible region corresponding to the InN mixed ratio, and therefore, are particularly important for display applications.
On the other hand, with the Group III-V compound semiconductor crystal layers as described above, an excellent crystal is not obtained in bulk growth, because homo-epitaxial growth using itself as a substrate material is difficult. Therefore, hetero-epitaxial crystal growth is generally conducted on a substrate, which is a different material from the material of crystal layers grown thereon. Since the number of substrates showing lattice conformity is small, however, in general, substrates such as α-alumina (lattice non-conformity 13.8%), silicon carbide (lattice mismatch 3.4%), ZnO (lattice non-conformity 2.0%), silicon (lattice non-conformity 20.4%), and the like showing more significant lattice non-conformity, are used under actual conditions.
It is known that with crystals thus grown by hetero-epitaxial growth, growth of a single crystal of large area is very difficult, and many defects are contained therein. In general, when a semiconductor material is used as a light-emitting device, crystal defects and impurities form a non-radiation center, exerting a reverse influence on properties, such as light-emitting efficiency and the like. Therefore, it is indispensable to reduce crystal defects and impurities as much as possible to improve crystallinity for use as a light-emitting device. There are reports on improvement in crystallinity by two-step growth in which a buffer layer made of AlN, GaN or the like having a thickness of 200 to 500 Å is grown, and a crystal is grown on this at high temperatures (see Japanese Laid-Open Patent Application Nos. JP 2-229476 A and JP 4-297023 A).